JP6558183B2 - Fixing device - Google Patents

Description

  The present invention relates to a fixing device that thermally fixes a developer image transferred to a recording sheet.

  As a fixing device used in an electrophotographic image forming apparatus, one that switches the nip pressure between a heating roller and a pressure roller in a plurality of stages using a motor and a cam is known (Patent Document 1). In this fixing device, the outer peripheral surface of the cam has two recesses with which a roller as a contact member engages. By engaging the roller with the recess, the direction of the cam is stabilized, and the nip portion The nip pressure is stabilized.

Japanese Patent No. 5481363

  By the way, in the conventional fixing device, the cam driving torque when changing the nip pressure, that is, the torque required when the roller moves from the concave portion of the outer peripheral surface of the cam is not taken into consideration. There was a risk that the torque would become unnecessarily large.

  SUMMARY An advantage of some aspects of the invention is that it provides a fixing device capable of suppressing an increase in cam driving torque while obtaining a stable nip pressure.

The present invention for solving the above problems is a fixing device for thermally fixing a developer image on a recording sheet, comprising a heating member, a backup member for sandwiching the recording sheet between the heating members, and a heating member. A support member that supports one of the backup members, a pressing member that presses the other of the heating member and the backup member against one of the heating member and the backup member, and a biasing member that biases the pressing member against the support member; A cam provided on one of the support member and the pressing member, and an abutting member provided on the other of the support member and the pressing member and having a curved surface that contacts the cam surface on the outer periphery of the cam.
The cam has a concave portion that comes into contact with and engages with the curved surface at least at two positions shifted in the rotational direction of the cam with respect to the curved surface, and the concave portion rotates with respect to the first concave portion and the first concave portion. And a second recess disposed away in the direction. The distance from the contact point on the most upstream side in the rotation direction to the rotation center of the cam in the first state where the curved surface is engaged with the first recess as viewed from the rotation axis direction of the cam is the first distance D1 and the rotation. The shortest distance from the center to the curved surface is the second distance D2, and the distance from the contact point on the most upstream side in the rotational direction to the rotational center in the second state where the curved surface is engaged with the second recess is the third distance D3, When the shortest distance from the center of rotation to the curved surface is the fourth distance D4,
D4> D2
And,
D3-D4 <D1-D2
Meet.

  According to such a configuration, since the direction of the cam is stabilized by the engagement of the contact member with the concave portion of the cam surface, the holding force (nip pressure) of the recording sheet of the heating member and the pressure member is stabilized. Can do. Further, since D4> D2, the cam moves the contact member in the second state so as to move away from the rotation center of the cam against the urging force of the urging member by a larger distance than in the first state. Let Therefore, in the second state, the urging force of the urging member is large, and in order to further rotate the cam from the second state, a larger force is required than in the case of rotating the cam from the first state. Since D4 <D1-D2, that is, in the second state, the drop of the concave portion that the curved surface of the contact member should overcome on the upstream side in the rotational direction of the cam (rear in the rotational direction) is smaller than in the first state. Compared to the case where the head is the same, the driving torque of the cam can be reduced. For this reason, it can suppress that the drive torque of a cam becomes unnecessarily large.

  According to the present invention, it is possible to stabilize the nip pressure and to suppress an increase in cam driving torque.

1 is a diagram illustrating a schematic configuration of a laser printer including a fixing device according to an embodiment of the present invention. 1 is a diagram illustrating a schematic configuration of a fixing device according to an embodiment of the present invention. It is a perspective view of a guide member. 2 is an exploded perspective view of main components of the fixing device. FIG. It is an enlarged view of a cam and a contact member. FIG. 3 is a side view of the fixing device in a normal nip state. 4A is a side view of the fixing device in a weak nip state, and FIG. 4B is an enlarged view showing a state where a roller enters a first recess. 4A is a side view of the fixing device in a nip release state, and FIG. 4B is an enlarged view showing a state where a roller enters a second recess. It is. FIG. 10 is a side view of a fixing device according to a modified example.

  Next, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. In the following description, the schematic configuration of the laser printer 1 (image forming apparatus) including the fixing device 100 according to the embodiment of the present invention will be described first, and then the detailed configuration of the fixing device 100 will be described.

<Schematic configuration of laser printer>
As shown in FIG. 1, the laser printer 1 includes a main body housing 2 in which a paper sheet 3 as an example of a recording sheet is fed, an exposure device 4, and a toner image (developer) on the paper P. And the fixing device 100 for thermally fixing the toner image on the paper P.

  In the following description, the direction will be described with reference to the user who uses the laser printer. That is, the right side in FIG. 1 is “front”, the left side is “rear”, the front side is “left”, and the back side is “right”. Also, the vertical direction in FIG.

  The paper feed unit 3 is provided in the lower part of the main body housing 2, and includes a paper feed tray 31 that accommodates the paper P, a paper pressing plate 32 that lifts the front side of the paper P, a paper feed roller 33, and a paper feed pad 34. And paper dust removing rollers 35 and 36 and a registration roller 37 are mainly provided. The paper P in the paper feed tray 31 is brought close to the paper feed roller 33 by the paper pressing plate 32 and separated one by one by the paper feed roller 33 and the paper feed pad 34, and the paper dust removing rollers 35 and 36 and the registration roller 37. Then, it is conveyed toward the process cartridge 5.

  The exposure apparatus 4 is arranged at the upper part in the main body housing 2 and mainly includes a laser light emitting unit (not shown), a polygon mirror 41 that is rotationally driven, lenses 42 and 43, and reflecting mirrors 44, 45, and 46. In preparation. In the exposure apparatus 4, the laser light (see the chain line) based on the image data emitted from the laser light emitting part is reflected or passed through the polygon mirror 41, the lens 42, the reflecting mirrors 44 and 45, the lens 43 and the reflecting mirror 46 in this order. The surface of the photosensitive drum 61 is scanned at high speed.

  The process cartridge 5 is disposed below the exposure apparatus 4 and is detachably mounted on the main body housing 2 through an opening formed when the front cover 21 provided on the main body housing 2 is opened. Yes. The process cartridge 5 includes a drum unit 6 and a developing unit 7.

  The drum unit 6 mainly includes a photosensitive drum 61, a charger 62, and a transfer roller 63. The developing unit 7 is configured to be detachably attached to the drum unit 6, and includes a developing roller 71, a supply roller 72, a layer thickness regulating blade 73, and a toner that contains toner (developer). The housing part 74 is mainly provided.

  In the process cartridge 5, the surface of the photosensitive drum 61 is uniformly charged by the charger 62 and then exposed by high-speed scanning of the laser light from the exposure device 4, whereby image data is transferred onto the photosensitive drum 61. An electrostatic latent image based on is formed. Further, the toner in the toner container 74 is supplied to the developing roller 71 via the supply roller 72 and enters between the developing roller 71 and the layer thickness regulating blade 73 to form a thin layer of a certain thickness on the developing roller 71. It is carried on.

  The toner carried on the developing roller 71 is supplied from the developing roller 71 to the electrostatic latent image formed on the photosensitive drum 61. As a result, the electrostatic latent image is visualized and a toner image is formed on the photosensitive drum 61. Thereafter, the paper P is conveyed between the photosensitive drum 61 and the transfer roller 63, whereby the toner image on the photosensitive drum 61 is transferred onto the paper P.

  The fixing device 100 is provided behind the process cartridge 5. The toner image (toner) transferred onto the paper P is thermally fixed onto the paper P by passing through the fixing device 100. The paper P on which the toner image is thermally fixed is discharged onto the paper discharge tray 22 by the transport rollers 23 and 24.

<Detailed configuration of fixing device>
As shown in FIG. 2, the fixing device 100 mainly includes a heating member 101 and a pressure roller 150 as an example of a backup member. The heating member 101 includes a fixing belt 110, a halogen lamp 120 as an example of a heating element, a nip plate 130 as an example of a nip member, a reflecting plate 140, and a stay 160.

  The fixing belt 110 is an endless (cylindrical) belt having heat resistance and flexibility, and both ends thereof are guided to rotate by guide members 170 described later.

  The halogen lamp 120 is a heating element that heats the toner on the paper P by heating the nip plate 130 and the fixing belt 110, and has a predetermined interval from the inner surface of the fixing belt 110 and the nip plate 130 inside the fixing belt 110. It is arranged with a gap.

  The nip plate 130 is a plate-like member that receives radiant heat from the halogen lamp 120, and is disposed so as to be in sliding contact with the inner surface of the cylindrical fixing belt 110. The nip plate 130 transmits the radiant heat received from the halogen lamp 120 to the toner on the paper P via the fixing belt 110.

  The reflection plate 140 is a member that reflects the radiant heat from the halogen lamp 120 (mainly radiant heat radiated in the front-rear direction and the upward direction) toward the nip plate 130, and the halogen lamp 120 is reflected inside the fixing belt 110. It is arranged at a predetermined interval from the halogen lamp 120 so as to surround it.

  The pressure roller 150 is a member that forms a nip portion N1 with the fixing belt 110 by sandwiching the fixing belt 110 and the paper P with the nip plate 130, and is disposed below the nip plate 130. Yes.

  The pressure roller 150 is configured to be rotationally driven by a driving force transmitted from a motor M provided in the main body housing 2, and to rotate with the fixing belt 110 (or paper P). The fixing belt 110 is driven to rotate by the frictional force. The sheet P on which the toner image is transferred is conveyed between the pressure roller 150 and the heated fixing belt 110 (nip portion N1), whereby the toner image is thermally fixed.

  The stay 160 is a member that ensures the rigidity of the nip plate 130 by supporting both ends of the nip plate 130 in the front-rear direction via the reflection plate 140. The stay 160 has a shape (substantially U shape in cross section) along the outer surface shape of the reflecting plate 140 and is disposed so as to cover the reflecting plate 140.

  The stay 160 holding the nip plate 130 and the reflecting plate 140 and the halogen lamp 120 are directly fixed to the guide member 170 shown in FIG. That is, the guide member 170 integrally supports the nip plate 130, the reflection plate 140, the stay 160, and the halogen lamp 120.

  The guide members 170 are formed of an insulating material such as resin, and are arranged one by one on both ends of the fixing belt 110, and mainly restrict the movement of the fixing belt 110 in the left-right direction (axial direction). . Specifically, the guide member 170 includes a restriction surface 171 that restricts the movement of the fixing belt 110 in the left-right direction, a suppression portion 172 that suppresses deformation of the fixing belt 110 inward in the radial direction, and both ends of the stay 160. Is mainly provided with a holding recess 173.

  The holding recess 173 is a groove that opens downward and penetrates in the left-right direction. A pair of side walls 174 opposed in the front-rear direction among the walls forming the holding recess 173 are formed with guide grooves 174A extending vertically.

  As shown in FIG. 4, the fixing device 100 supports a fixing frame 180 as an example of a supporting member, a pair of swing arms 190 as an example of a pressing member, and a pressing member fixed to the main body housing 2. A pair of tension springs 198 as an example of a biasing member that biases the member and a pair of left and right cams 200 connected by a shaft 201 are provided.

  The fixing frame 180 is a member that rotatably supports the pressure roller 150 and guides the vertical movement of the heating member 101. The fixing frame 180 includes a pair of left and right side walls 181 and a connecting portion 182 that connects the pair of side walls 181. Prepare. Each side wall 181 has a concave portion 181A recessed downward from the upper end, and a semicircular bearing portion 181B is formed at the bottom of the concave portion 181A. Each bearing part 181B is fitted with a U-shaped bearing member 183, and each bearing part 181B supports the shaft 151 of the pressure roller 150 from below through the bearing member 183.

  An upper portion of the recess 181A of each side wall 181 forms a rail 181C extending straight in the vertical direction. Each rail 181C can move the heating member 101 up and down along the rail 181C by fitting the guide grooves 174A of the guide members 170 at the left and right ends of the heating member 101.

  A support hole 185 for rotatably supporting the shaft 201 of the cam 200 is formed on the front side of the recess 181A of each side wall 181. Further, on the left and right outer surfaces of each side wall 181, a support shaft 184 for swingably supporting the swing arm 190, a stopper 186 for restricting the downward movement of the swing arm 190, and a tension spring 198 are provided. A spring hooking portion 187 for hooking the lower end of the head is provided so as to protrude (only one on the right side is shown).

  Each swing arm 190 is formed of a long and narrow plate-like member extending in the front-rear direction, and has a hole 191 formed at the rear end. The hole 191 engages with the support shaft 184 of the fixing frame 180, thereby It is supported so that it can swing. A contact portion 192 bulging in an arc shape is formed on the lower surface of each swing arm 190. The contact portion 192 contacts the upper surface 175 of the guide member 170 and supports the heating member 101 so as to press the guide member 170 from above. A hook 193 that hooks the upper end of the tension spring 198 is formed at the front end of the swing arm 190. A roller 194 protrudes from the left and right outer surfaces of the swing arm 190 between the contact portion 192 and the hook 193 in the front-rear direction. The roller 194 is rotatable with respect to the swing arm 190 and has a cylindrical surface 194 </ b> A as a curved surface capable of coming into contact with the cam surface 202 which is the outer peripheral surface of the cam 200 on the outer periphery.

  The motor M for driving the pressure roller 150 is connected to the pressure roller 150 via a first transmission mechanism (not shown), and is controlled by a control device (not shown) and a second clutch (not shown). It is connected to the cam 200 via a transmission mechanism. That is, the motor M for driving the cam 200 is used for driving the pressure roller 150 which is an element different from the cam 200. The control device is configured to control the motor M and the clutch 209, connect the clutch 209 only at a necessary time at a necessary timing, and rotate the cam 200 in one direction by using the driving force of the motor M. Has been.

As shown in an enlarged view in FIG. 5, the cam 200 has two recesses on the cam surface 202, and a cam rotation direction (clockwise in FIG. 5) with respect to the first recess 210. , Hereinafter referred to simply as “rotation direction”). When viewed from the direction of the cam rotation axis 201A (hereinafter simply referred to as “rotation axis direction”), the first recess 210 has an arc shape with a radius R1, and the second recess 220 has an arc shape with a radius R2. Have. On the other hand, the cylindrical surface 194A of the roller 194 has a circular shape with a radius R3 when viewed from the rotational axis direction. R1, R2 and R3 are
R3>R2> R1
Meet the relationship. For this reason, the first recess 210 contacts and engages with the cylindrical surface 194A at two positions (contact point P1 and contact point P2) shifted in the rotation direction of the cam 200, and the second recess 220 is formed with the cylindrical surface. 194A comes into contact with and engages at two locations (contact point P3 and contact point P4) that are shifted in the rotational direction of the cam 200.

Then, in the first state where the cylindrical surface 194A is engaged with the first recess 210 (see the roller 194 indicated by a broken line), the rotation axis 201A that is the rotation center of the cam 200 from the contact point P1 on the most upstream side in the rotation direction. Is the first distance D1, the shortest distance from the rotation axis 201A to the cylindrical surface 194A is the second distance D2, and the second state in which the cylindrical surface 194A is engaged with the second recess 220 (the roller indicated by the two-dot chain line) 194)), the distance from the contact point P3 on the most upstream side in the rotation direction to the rotation axis 201A is the third distance D3, and the shortest distance from the rotation axis 201A to the cylindrical surface 194A is the fourth distance D4. , D2, D3 and D4 are
D4> D2
And,
D3-D4 <D1-D2
Meet.

  That is, the drop D3-D4 that the roller 194 in the second state must get over the contact point P3 on the upstream side in the rotational direction is the same as the drop D3-D4 that the roller 194 in the first state gets over the contact point P1 on the upstream side in the rotational direction. It is smaller than the drop D1-D2 that must be present.

Further, the distance from the contact point P1 on the most upstream side in the rotation direction to the contact point P2 on the most downstream side in the rotation direction is the fifth distance D5, and the rotation in the second state when viewed from the 200 rotation axis direction of the cam. Assuming that the distance from the contact point P3 on the most upstream side in the direction to the contact point P4 from the most downstream side in the rotational direction is a sixth distance D6, D5 and D6 are
D5> D6
Meet.

  That is, the amount that has entered the first recess 210 in the first state (the amount by which the roller 194 has entered the rotation axis 201A side with respect to the line segment P1-P2) has entered the second recess 220 in the second state. Larger than the amount (the amount of the roller 194 entering the rotation axis 201A side with respect to the line segment P3-P4).

Further, when viewed from the rotation axis direction of the cam 200, the distance from the contact point P2 on the most downstream side in the rotation direction in the first state to the rotation axis line 201A is the seventh distance D7, and the contact point on the most downstream side in the rotation direction in the second state. Assuming that the distance from P4 to the rotation axis 201A is the eighth distance D8, D1, D7, D3 and D8 are:
D1 ≧ D7
And D3 ≧ D8
Meet.

  In addition, the rotation of the cam 200 is controlled by the control device, so that during normal printing, the roller 194 is maintained in the position indicated by the solid line in FIG. In this state, the cam surface 202 of the cam 200 is separated from the roller 194, and this is the third state. In the third state, the facing surface portion 230 facing the cylindrical surface 194A of the cam surface 202 is formed in a flat shape. In the third state in which the facing surface portion 230 faces the cylindrical surface 194A, the cam 200 does not push up the roller 194. Therefore, the clamping force between the heating member 101 and the pressure roller 150 is the same as that of the heating member 101 in the first state. It is larger than the clamping force of the roller 150. In the second state, the lift amount of the cam 200 in the second recess 220, that is, the third distance D3 and the eighth distance D8 is set so that the heating member 101 is separated from the pressure roller 150.

  The cam 200 is configured such that the rotation angle α of the cam 200 from the first state to the second state is larger than the rotation angle β of the cam 200 from the third state to the first state. For this reason, even if it is necessary to lift the roller 194 greatly when the state transitions from the first state to the second state, the rotation torque of the cam 200 is excessively increased because the roller 194 is lifted using a large rotation angle. It is possible to suppress.

  The operation of the fixing device 100 in the laser printer 1 configured as described above will be described. As shown in FIG. 6, in the third state corresponding to normal printing, the facing surface portion 230 faces the cylindrical surface 194A of the roller 194, and the cam surface 202 is separated from the cylindrical surface 194A. For this reason, the cam 200 does not hinder the force by which the tension spring 198 urges the swing arm 190 downward (part of the fixing frame 180 that supports the pressure roller 150). Therefore, the posture of the swing arm 190 is determined by the lower surface of the hook 193 that is the tip of the swing arm 190 being in contact with the upper surface of the stopper 186. Then, the contact portion 192 contacts the upper surface 175 of the guide member 170 and urges the guide member 170 downward. For this reason, the nip plate 130 and the fixing belt 110 of the heating member 101 are urged by the pressure roller 150 to form a nip portion N <b> 1 between the pressure roller 150. At this time, since the urging force of the tension spring 198 is not suppressed by the cam 200, the nip width of the nip portion N1 becomes relatively large. This state is called a strong nip state.

  When the motor M is driven by the control device and the clutch 209 is connected for a predetermined period, the cam 200 rotates clockwise from the state shown in FIG. 6, and the cam 200 moves on the cam surface 202 as shown in FIG. The roller 194 is pushed up, and the roller 194 engages with the first recess 210. When the roller 194 engages with the first recess 210, the direction of the cam 200 is stabilized, and the clamping force between the heating member 101 and the pressure roller 150 can be stabilized.

  In this operation, since the roller 194 can rotate, the roller 194 rolls on the cam surface 202, and thus smoothly transitions from the third state to the first state. As shown in FIG. 7B, when the roller 194 engages with the first recess 210, the first distance D1 is equal to or greater than the seventh distance D7, so that the roller 194 exceeds the contact point P2. When entering the first recess 210, the amount that falls into the first recess 210 is relatively small. For example, if the first distance D1 is smaller than the seventh distance D7, the roller 194 is greatly lifted by the cam 200 in order to get over the contact point P2, and then the lift amount is greatly reduced to contact the contact point P1 and the contact point P2. As a result of contacting and stopping both, a large impact is generated when hitting the contact point P1, but in the fixing device 100 of the present embodiment, the first distance D1 is equal to or greater than the seventh distance D7. Since 194 hits the contact point P1 and stops while entering the first recess 210 at a relatively slow speed, the impact can be reduced.

  In the state of FIG. 7A, since the cam 200 slightly lifts the roller 194, the heating member 101 is slightly raised by the elastic force of the pressure roller 150 as compared with the strong nip state of FIG. Thus, a nip portion N2 having a small nip width is formed. This state is called a weak nip state.

  Then, when the motor M is further driven by the control device from the first state of FIG. 7A and the clutch 209 is connected for a predetermined period, the cam 200 rotates clockwise. On the other hand, paying attention to the roller 194, the roller 194 rolls counterclockwise with respect to the cam 200, moves over the contact point P1, and moves counterclockwise on the cam surface 202. Then, as shown in FIG. 8A, the cam 200 rotates clockwise, and the cam 200 lifts the roller 194 with the cam surface 202. The roller 194 moves smoothly while rolling counterclockwise on the cam surface 202, and the roller 194 engages with the second recess 220. That is, the cam 200 sequentially changes from the third state to the second state via the first state due to the rotation thereof. Then, when the roller 194 is engaged with the second recess 220, the direction of the cam 200 is stabilized, and the clamping force between the heating member 101 and the pressure roller 150 can be stabilized.

  Further, as shown in FIG. 8B, when the roller 194 engages with the second recess 220, the third distance D3 is equal to or greater than the eighth distance D8, so that the roller 194 exceeds the contact point P4. When entering the second recess 220, the amount that falls into the second recess 220 is relatively small. Therefore, the roller 194 slowly hits the contact point P3 and stops, so that the impact can be reduced.

  In the state of FIG. 8A, since the cam 200 lifts the roller 194 greatly, the contact portion 192 of the swing arm 190 and the upper surface 175 of the guide member 170 are separated from each other. For this reason, compared with the weak nip state of FIG. 7, the heating member 101 is further raised and contacts the pressure roller 150 only by its own weight. For this reason, it is possible to easily perform jam processing of the paper P jammed between the heating member 101 and the pressure roller 150. This state is called a nip release state.

  Then, when the motor M is further driven by the control device from the second state of FIG. 8A and the clutch 209 is connected for a predetermined period, the cam 200 rotates clockwise. On the other hand, paying attention to the roller 194, the roller 194 rolls counterclockwise with respect to the cam 200, moves over the contact point P3, and moves counterclockwise while rolling on the cam surface 202. Then, the cam 200 rotates clockwise, and the lift amount of the cam 200 gradually decreases, so that the roller 194 is lowered. Thereafter, as shown in FIG. 6, when the roller 194 faces the facing surface portion 230, the roller 194 is separated from the cam surface 202 and returns to the third state, and the heating member 101 and the pressure roller 150 return to the strong nip state. .

  In the above rotation operation of the cam 200, since D4> D2, the urging force of the tension spring 198 in the second state is larger than the urging force in the first state. For this reason, in order to rotate the cam 200 from the second state to the third state, a larger force is required than when rotating the cam 200 from the first state to the second state. However, according to the embodiment, the difference D3-D4 between the third distance D3 and the fourth distance D4 is set smaller than the difference D1-D2 between the first distance D1 and the second distance D2. That is, when the transition from the second state to the third state occurs, the drop D3-D4 of the recess that the roller 194 has to overcome must be overcome when the transition from the first state to the second state occurs. Since it is smaller than the drop D1-D2 of the recess that should not be made, the driving torque of the cam 200 can be made smaller than when the drop is the same. For this reason, it can suppress that the drive torque of the cam 200 becomes unnecessarily large, and can reduce the load of the motor M.

  Although the embodiment of the present invention has been described above, the present invention is not limited to the embodiment. About a concrete structure, it can change suitably in the range which does not deviate from the meaning of this invention.

  In the above-described embodiment, the cam 200 lifts the roller 194 to lift the swing arm 190 and weaken the clamping force between the heating member 101 and the pressure roller 150. It can also be configured to increase the clamping force between the heating member 101 and the pressure roller 150 by lifting. For example, in the fixing device 300 according to the modification shown in FIG. 9, the cam 200 is disposed above the roller 194, and the tension spring 198 is disposed so as to pull up the swing arm 190. In such a configuration, when the roller 194 engages with the second recess 220 and is most lifted, a strong nip state occurs, and when the roller 194 engages with the first recess 210 and slightly lifts, the weak nip state occurs. When the roller 194 faces the facing surface portion 230, the nip release state is established.

  In the above embodiment, the roller 194 is exemplified as the contact member, but the contact member may be a protrusion that does not rotate. In this case, the curved surface of the contact member that comes into contact with the cam surface may have a circular arc shape in cross section.

  In the above-described embodiment, the concave portion and the contact member are in contact with each other only at two locations separated in the cam rotation direction. However, the concave portion and the contact member may be in contact with each other at three or more locations. You may contact continuously over the range which connects two places which shifted | deviated to this rotation direction. Further, the concave portion is not limited to the circular arc shape in cross section, and may be a groove having a V-shaped cross section or a so-called trapezoidal cross-sectional groove having a flat portion at the bottom of the V-shaped groove.

  In the above-described embodiment, only the first concave portion and the second concave portion are shown as the concave portions provided in the cam, but three or more concave portions may be provided.

  In the embodiment, the roller 194 as a contact member is supported by the swing arm 190 and the cam 200 is supported by the fixing frame 180. Conversely, the cam 200 is supported by the swing arm 190 and the fixing frame is supported. A contact member may be provided at 180. The pressing member is not limited to the swing arm, and may be configured to slide relative to the support member. The pressing member may be fixed to the housing of the image forming apparatus, and the support member may be moved relative to the housing. In the embodiment, the fixing frame 180 is described as an example of the support member. However, in addition to the fixing frame 180, the fixing frame 180 is fixed to the main body housing 2 to which the fixing frame 180 is fixed. It can also be seen that the member is part of the support member. For example, a cam may be provided on the main body housing 2 as a part of the support member or a member fixed to the main body housing 2, or one end of the biasing member may be fixed.

  In the above embodiment, the fixing member is used as the heating member. However, a rotating heating roller may be used. Further, although the pressure roller 150 is exemplified as the backup member, a belt-like pressure member or the like may be used.

  In the above embodiment, the recording sheet is exemplified by plain paper or postcard, but may be OHP sheet.

  In the above embodiment, the laser printer 1 is exemplified as the image forming apparatus including the fixing device of the present invention. However, the present invention is not limited to this, and may be, for example, an LED printer that performs exposure using LEDs. A copying machine other than a printer or a multifunction machine may be used. In the above-described embodiment, an image forming apparatus that forms a monochrome image is exemplified. However, the present invention is not limited to this, and an image forming apparatus that forms a color image may be used.

DESCRIPTION OF SYMBOLS 1 Laser printer 100 Fixing device 101 Heating member 110 Fixing belt 150 Pressure roller 170 Guide member 180 Fixing frame 190 Oscillating arm 194 Roller 194A Cylindrical surface 198 Tensile spring 200 Cam 201A Rotation axis 202 Cam surface 209 Clutch 210 First recess 220 Second 2 concave portion 230 facing surface portion M motor P1 to P4 contact point

Claims (10)

A fixing device for thermally fixing a developer image on a recording sheet,
A heating member;
A backup member for sandwiching the recording sheet with the heating member;
A support member that supports one of the heating member and the backup member;
A pressing member that presses the other of the heating member and the backup member against one of the heating member and the backup member;
A biasing member that biases the pressing member against the support member;
A cam provided on one of the support member and the pressing member;
An abutting member provided on the other of the support member and the pressing member and having a curved surface that comes into contact with the cam surface on the outer periphery of the cam;
The cam has a recess that contacts and engages the cam surface at least at two positions that are shifted in the rotation direction of the cam with respect to the curved surface.
The recess includes a first recess and a second recess disposed away from the first recess in the rotational direction,
Seen from the rotational axis direction of the cam,
In the first state where the curved surface is engaged with the first recess, the distance from the contact point on the most upstream side in the rotation direction to the rotation center of the cam is the first distance D1, and the shortest distance from the rotation center to the curved surface Is the second distance D2, and in the second state where the curved surface is engaged with the second recess, the distance from the contact point on the most upstream side in the rotation direction to the rotation center is the third distance D3, and the rotation center is When the shortest distance to the curved surface is the fourth distance D4,
D4> D2
And,
D3-D4 <D1-D2
A fixing device characterized by satisfying the above. The distance from the contact point on the most upstream side in the rotation direction to the contact point on the most downstream side in the rotation direction in the first state when viewed from the rotation axis direction of the cam is a fifth distance D5, and the distance in the second state The distance from the contact point on the most upstream side in the rotation direction to the contact point on the most downstream side in the rotation direction is defined as a sixth distance D6.
D5> D6
The fixing device according to claim 1, wherein: When viewed from the rotational axis direction of the cam, the distance from the contact point on the most downstream side in the rotation direction in the first state to the rotation center is a seventh distance D7, and the contact on the most downstream side in the rotation direction in the second state. The distance from the point to the center of rotation is the eighth distance D8,
D1 ≧ D7
The fixing device according to claim 2, wherein D3 ≧ D8 is satisfied.   The first recess contacts and engages with the curved surface at two locations shifted in the rotation direction of the cam, and the second recess contacts with the curved surface at two locations shifted in the rotation direction of the cam. The fixing device according to claim 1, wherein the fixing device is engaged. When viewed from the rotation axis direction of the cam, the first recess has an arc shape with a radius R1, the second recess has an arc shape with a radius R2, and the curved surface has a radius R3.
R3>R2> R1
5. The fixing device according to claim 1, wherein the fixing device satisfies the following condition.   The state where the cam is separated from the contact member is a third state, and the holding force between the heating member and the backup member in the third state is greater than the holding force between the heating member and the backup member in the first state. 6. The fixing device according to claim 1, wherein in the second state, the heating member is separated from the backup member. 7.   The fixing device according to claim 6, wherein the cam rotates in a direction in which the cam sequentially shifts from the third state to the second state via the first state.   The fixing device according to claim 7, wherein a rotation angle of the cam from the first state to the second state is larger than a rotation angle of the cam from the third state to the first state. .   The fixing device according to claim 1, further comprising a motor that rotationally drives the cam, wherein the motor is used to drive another element different from the cam.   The fixing device according to claim 1, wherein the contact member is a roller rotatably supported on one of the support member and the pressing member.

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